Date

Dates are specified as a string in the format of y/m/w (year, month, week) = for example 13/2/3.

Based on the game settings Game Dev Tycoon can run in different game length modes:

game length	gameLengthModifier
30 years	1
35 years (default game length)	1.16667
42 years	1.4

By default, the game runs for 35 years which, for historical reasons, is implemented by setting the gameLengthModifier to 1.16667.

You don't have to worry about the modifier in code but when defining dates on an event (GDT.addEvent) for example, you need to be aware that all dates in code are based on a gameLengthModifier of 1. This means that if you define a date as 30/1/1 and a player is playing with the default game length setting, the event will actually fire on 35/1/1. If the player would play the 42 year version it would fire on 42/1/1. (You can disable this for events by setting the event.ignoreGameLengthModifier to true.)